Session S05: Atom Interferometry II

Atom interferometry aboard the International Space Station

Bose-Einstein condensates (BECs) are excellent systems for quantum sensing applications like navigation, relativistic geodesy and tests of the universality of free fall. The sensitivity of most such atom interferometers increases quadratically with the interrogation time, which makes it beneficial to extend the free fall time. To accomplish this goal NASA has launched the Cold Atom Lab (CAL) [1,2] to the International Space Station enabling atom interferometers with BECs in orbit.

Here we report on a series of experiments performed on CAL, using different interferometer geometries to measure any residual magnetic or inertial forces acting on the atom cloud. Furthermore, we discuss current limitations as well as prospective future experiments on CAL. These results pave the way towards future precision measurements with atom interferometers in space.   

Sagnac atom interferometer gyroscope with large enclosed area and multiple orbits

Sagnac atom interferometers are a promising technique for high-performance rotation sensing, with potential applications for inertial navigation. The use of trapped atoms for the interferometer avoids the need for long free-fall distances that would be incompatible with a navigation apparatus. We have previously demonstrated a dual Sagnac interferometer using Bose-condensed atoms in a time-orbiting potential trap. We report here on improvements to this approach, including a 3-fold increase in the orbit radius and the use of multiple orbits. These improvements lead to an enclosed area of 6.6 mm², which corresponds to a rotation sensitivity of 6×10^-7 rad/s at shot-noise-limited detection. While shot-noise-limited performance has not yet be achieved, the interferometer operation is sufficiently stable to permit useful averaging times longer than 10⁴ s. We also discuss a new, more compact, version of the apparatus that is based on an atom chip and which will be suitable for environmental testing.

    

Atom interferometric gravity data acquisition with the transportable absolute Quantum Gravimeter QG-1

The transportable Quantum Gravimeter QG-1 derives the local gravity value from the interferometric signal of magnetically collimated Bose-Einstein condensates (BECs) released into free-fall and read out by absorption imaging. It aims to determine the gravity value with an uncertainty < 3 nm/s^2, an order of magnitude below the uncertainty of cold atom gravimeteres [1-3]. The minimized initial velocity and expansion rate of the collimated BEC, produced with our atom-chip-based source, enables the projected increase in accuracy. Employing BECs allows to drive high contrast interferometers with higher order Bargg transitions increasing the interferometer sensitivity. A BEC sample gives rise to additional systematic effects i.e. phase shifts driven by the mean field energy. Further the atom chip induces shifts stemming from black-body radiation. We discuss these effects and introduce the overall setup.

(1) C. Freier et al., J. Phys. Conf. Ser. 723

(2) R. Karcher,  et al., New J. Phys 20.11

(3) A. Louchet-Chauvet et al., New J. Phys. 13   

The QUANTUS Project- Theory in the Ulm Group Investigating the properties of Bose-Einstein condensates under microgravity conditions and developing methods for atom interferometry.

Atom interferometry provides a unique opportunity not only for probing the foundations of physics at the interplay of relativity and quantum theory, but also for devising diverse, compact applications like sensors. In this spirit, the long-standing and fruitful QUANTUS collaboration investigates the dynamics of Bose-Einstein condensates under microgravity conditions and its application to atom interferometry. In particular, the QUANTUS theory group in Ulm focuses on a fundamental modelling of the light-matter dynamics, its impact on interferometric experiments, as well as potential setups to improve sensitivitity in the test of relativistic physics and fundamental principles. In this contribution, we will present an overview of the current work of the QUANTUS theory group in Ulm, and provide a perspective on upcoming projects of the newly starting QUANTUS+ collaboration.   

Full 3D Simulations of Guided BEC Interferometers

Atom interferometry has grown into a successful tool for precision measurements since the pioneering works of  Steven Chu and Mark Kasevich [1, 2]. Experiments with record-breaking precision have been performed in the fields of inertial sensing and tests of the foundations of physics. These high precision measurements are achieved either by large momentum transfer (LMT) or long interrogation times. Recently, the former technique has led to a state-of-the-art separation of more than 400 hbark [3]. In this experiment, Bose-Einstein Condensates (BECs) are used to further enhance precision atom interferometry thanks to the intrinsically large coherence and narrow momentum width. In this talk, we present a newly developed numerical toolbox to solve the time-dependent Gross-Pitaevskii equation in 3D. To demonstrate its capability, we study BEC interferometers realized in both free-fall and guided geometry and compare our results with experimental data. We specifically investigate the guided expansion and double-Bragg diffraction (DBD) of a BEC by two retro-reflected laser beams in a real-time evolution. Finally, we present a phase scan of a fully guided Mach-Zehnder interferometer based on DBD.

[1] Kasevich M. and Chu S., Phys. Rev. Lett., 67 (1991) 181.

[2] Kasevich M. and Chu S., Appl. Phys. B, 54 (1992) 321.

[3] Gebbe, M., Siemß, JN., Gersemann, M. et al., Nat Comm., 12, (2021) 2544.   

Tractor atom interferometer

Tractor Atom Interferometer (TAI), a recently proposed matter-wave interferometer, features uninterrupted three-dimensional confinement and transport of atomic wave-packets along programmable trajectories using optical or other traps. We present numerical investigations on rotation sensing using TAI with a multi-pass design for scalable sensitivity. From our numerical quantum dynamics simulations we infer the sensitivity and confirm agreement with semiclassical predictions, in the adiabatic limit. Our results demonstrate robust suppression of wave-packet dispersion, tunneling and non-adiabatic excitations in the TAI performance over a wide range of parameters and multiple transport loops   

Scale factor corrections for point source atom interferometry

 Point source atom interferometry (PSI) is a promising candidate for realizing compact, high-sensitivity inertial sensors. Here, we present results on a magneto-optical trap-based PSI atom interferometer using ⁸⁷Rb and methods to improve the scale factor stability for rotation sensing. Scale factors in PSI are dependent on the initial cloud shape and size, and analytic corrections to the scale factor exist for Gaussian density profiles. We present work developing corrections for arbitrary initial cloud shapes and discuss the relative benefits for overall gyroscope stability.   

Cold and Continuous Atom Interferometer for Inertial Sensing

We present new measurements of a continuous atomic interferometer designed for inertial sensing. The interferometer is derived from an atom source which emits a continuous beam of sub-Doppler cooled atoms while simultaneously mitigating near-resonant scattered light. Enabled by the unique properties of the atom source, the derived interferometer demonstrates continuous measurement exhibiting high contrast and low noise. We describe unique and useful features of our apparatus, such as continuous phase shear readout, and rapid switching of intertial sensitivity, much faster than the characteristic time-scale of a typical matter-wave interferometer. Our work here inspires future cold-atom architectures which can measure with both high sensitivity and high bandwidth.   

Novel Light Field Imaging Device with Enhanced Light Collection for Cold Atom Clouds

We present a light field imaging system that captures multiple views of the target object with a single shot. The system also maximizes the total light collection, by accepting a larger solid angle of light than a conventional lens with equivalent depth of field characteristics, and retains high resolution over the target's span. Simulation results demonstrate that this system is capable of single-shot tomography of atom clouds of size O(1mm), reconstructing the 3-dimensional (3D) distribution of atoms and features not accessible from any single view angle in isolation. In particular, for atom clouds used in atom interferometry experiments, the system can reconstruct 3D fringe patterns with size O(100µm). We also demonstrate this system with a prototype. The prototype is used to take images of O(1mm) sized objects, and 3D reconstruction algorithms running on a single-shot image successfully reconstruct O(100µm) features. The prototype also shows that the system can be deployed quickly and cost-effectively in experiments with needs for enhanced light collection or 3D reconstruction.